Mutations of MMR genes, MLH1, mutS homolog 2 (MSH2), mutS homolog 3 (MSH3), MSH6, postmeiotic segregation increased1 (PMS1) and PMS2, are involved in the pathological mechanism of Lynch syndrome [32,34] through inhibition of MMR during DNA replication, which leads to subsequent MSI and carcinogenesis [34]. This evidence concerns the gene PMS1 and Lynch syndrome.